1. Field of the Invention
This invention relates to a sustained release composition. More particularly, it is concerned with a sustained release composition using a hemicellulose extracted from wheat bran or a wheat bran extract predominantly containing the hemicellulose as a matrix having a property of releasing a chemical substance at a controlled rate.
2. Description of the Prior Art
Various approaches have been proposed to develop sustained release preparations, that is, preparations for retarding release of the active ingredient to allow the effect to be sustained over a prolonged time. For example, there are employed many methods including binding of the active ingredient with a binder poor in disintegration in digestive tracts and coating of the active ingredient with such a material as wax or a macromolecular substance. Among the methods for preparing such sustained release preparations, a cellulose derivative have recently called attention particularly in view of its sustained release function. There are disclosed sustained release preparations using a lower alkyl ether of cellulose as the matrix (Japanese Patent LOP Publication No. 286330/1986) and sustained release preparations using hydroxypropyl methylcellulose or the like (Japanese Patent LOP Publication No. 120315/1987).
On one hand, many attempts have been made hitherto to isolate in pure form hemicellulose contained in wheat bran and effectively use it. For example, an invention relating to use as anticholesteremic agent of hemicellulose produced by extracting wheat bran under alkaline conditions has been proposed in Japanese Patent LOP Publication No. 41824/1983. We have proposed a method for extracting and purifying hemicellulose useful as fibrous food which comprises extracting wheat bran under weak alkaline conditions.
Since the cellulose derivatives used as a matrix in sustained release preparations of the prior art are semisynthetic products obtained by chemical modification of naturally occurring cellulose, a naturally occurring substance substitutable therefor will be preferred in consideration of safety, toxicity and other factors.
The cellulose derivatives used in the prior art methods such as lower alkyl ethers of cellulose and hydroxypropyl methylcellulose are somewhat hygroscopic so that they are defective in that they will absorb moisture in the air while being formed, for example, into tablets to become sticky and coating such as sugar coating is needed in order to avoid such a defect.
Therefore, sustained release preparations free from such defects have been desired.